Yaesu FL-2100B SWR in standby

Discussion in 'Amateur Radio Amplifiers' started by N8VIL, Jan 10, 2016.

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  1. W1QJ

    W1QJ Ham Member QRZ Page

    Add a 33pf 500v mica capacitor from the cross bar connection (on the NC contacts that are jumped) to ground and the problem will go away or be greatly reduced. This is a common problem with open frame relays. Some relays are better than others and from build to build like on Heathkit SB-220 amps. If you do this your problem will go away or be greatly reduced.
    WA7PRC likes this.
  2. N8VIL

    N8VIL Ham Member QRZ Page

    I will try that. I have that value SM capacitor in my stockpile. I have cleaned the relay contacts and re-soldered connections to no avail. I suspect that I may have to adjust input tuning after this modification.
  3. W1QJ

    W1QJ Ham Member QRZ Page

    No you won't. That capacitor is only in circuit on feed thru from radio to antenna when the relay is NC. WHen you actuate the relay that cap is out of circuit when the amp is being driven, so you don't have to change anything. Make sure you put the cap in the right place on the relay. There should be a bare wire connecting the NC connections of the relay in the receive mode. You connect the cap from there to ground. This will cancel the XL of the relay contacts which is giving you the feed thru swr.
  4. N8VIL

    N8VIL Ham Member QRZ Page

    Your right. After my last post I looked at the schematic. I will do this in the next few days and post how it worked out.
  5. VE3TMT

    VE3TMT XML Subscriber QRZ Page

    I just went through and checked SWR between exciter and amp with the dummy load in line. SWR is 1.0:1. One bar lighting on the SWR scale of the FT1000 Field. I swapped my original relay out last year for something a little quieter and rewired the input/output circuit at the same time.
  6. WA7PRC

    WA7PRC Ham Member QRZ Page

    The relay N8VIL has in his amplifier is a DPDT (aka "2-Form-C") type. The length of the arm plus the wire that connects it to its terminal makes the length between each NC terminal and COM terminal quite long. Then, add the wire between the two COM terminals. On 80m, that's not an issue but, on 10m, it starts to matter. That's the reason for the added shunt capacitance.

    Bryan WA7PRC
  7. AC8AC

    AC8AC Ham Member QRZ Page

    W1QJ is on target add some capacitive reactance to the relay to cancel out relay lead inductance .. large open frame relays with long lead lengths can cause this and it is seen in many older amplifiers

    ive had to do this in some of my home brews as well usually only takes a few pf to cancel it out .. my 6 meter home brew had a 2.2:1 i added 12pf and it was flat but i used a 40 amp relay in it probly should have used vacuum or dow key but im cheap . i had no measurable loss with what tooling i have so no harm no fowl
    WA7PRC likes this.
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Could probably use a small variable cap in lieu of the 33 pF fixed value and "fine tune" it on 10m...never tried that but seems likely it would work.
  9. W1QJ

    W1QJ Ham Member QRZ Page

    More often than not 33pf does the job. But anything within 5 pf of that may work as well. 33pf is the magic number for the SB-220 relays and Ameritron relays. The Amertron amps with the 3PDT relays all have this cap. You won't find it on the schematic, it's not there, but it is on the relay.
    WA7PRC likes this.
  10. G3YRO

    G3YRO Ham Member QRZ Page

    I'm not convinced it's just the relay itself . . . have you looked at the wiring underneath?

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